Word of Harper Lee’s first new novel in 55 years set the literary world on fire Tuesday with critics and fans speculating about the surprise sequel to Lee’s famous classic To Kill a Mockingbird.

Publisher Harper announced that Go Set a Watchman, a novel the Pulitzer Prize-winning author completed in the 1950s and put aside, will be released this year.

Fans exploded with excitement upon hearing about the existence of what would be Lee’s second novel ever.

"Harper Lee returns and there is joy throughout the land," tweeted American documentary filmmaker Michael Moore, "I've ordered mine."

Media mogul Oprah Winfrey issued a statement saying "I couldn't be happier if my name was Scout," referring to the young narrator in Mockingbird.

The work of 'an amateur'

But the book world bombshell also sparked skepticism. Harper revealed that the 304-page book will be published unedited, and that the deal was negotiated strictly between Lee’s lawyer and Harper's parent company, HarperCollins Publishers.

Lee biographer Charles J. Shields suggests fans might be disappointed by the book that hasn't been aided by an editor’s skilled revisions.

 “We’re going to see what Harper Lee writes like without a strong editor’s hand, when she’s, quite honestly, an amateur,” Shields told the New York Times. “It’s going to be very interesting to see how original it is. A lot was taken from Go Set a Watchman for To Kill a Mockingbird, and maybe those are the best parts."

Lee expressed her own "hesitation" to have the work released in a statement thorough her publisher.

"[I was] pleased to hear that they considered it worthy of publication," Lee wrote, "I am humbled and amazed that this will now be published after all these years."

Curious timing

Concerns over quality aside, some fans are worried that Lee might not have given adequate consent.

"Is someone taking advantage of our national treasure, 88-year-old Harper Lee?" tweeted American actress Mia Farrow.

The fiercely private writer has been living in an assisted-living centre since suffering a stroke in 2007. Alice Lee, the author’s older sister and her protective advocate, had been taking care of Lee and her estate for decades.  

Alice Lee died late last year, potentially leaving the 88-year-old vulnerable.

"[My sister] can’t see and can’t hear and will sign anything put before her by anyone in whom she has confidence," wrote Alice Lee in a 2011 letter to reporter and neighbour Marja Mills, whose memoir The Mockingbird Next Door was publicly contested by Lee and her lawyer.

The Mockingbird Next Door offered a rare glimpse into the life of the notoriously reclusive writer, and Lee repeatedly denied that she authorized its writing.

Despite the controversy, the book was eventually published in 2014 by publisher Penguin Press who released a letter affirming that Mills had cooperation from the Lee sisters in writing the book.

Bound to be a bestseller

Even with worries over readability, there is intense interest in Go Set the Watchman and that is bound to translate into blockbuster sales.

Lee's To Kill a Mockingbird is a high school reading list standard and among the most beloved novels in history.

It also has worldwide sales topping 40 million copies. 

The new book is set in Lee's famed Maycomb, Alabama, during the mid-1950s, 20 years after To Kill a Mockingbird and roughly contemporaneous with the time that Lee was writing the story. It also features the character known as Scout, but now she is an adult woman.

Go Set the Watchman will hit store shelves and electronic readers on July 14.

With files from The Associated Press